Method and system for routing in an ATM network

ABSTRACT

for The present invention relates to a method and system for routing in an ATM network comprising a plurality of nodes connected to each other via links, a network management center being connected to said ATM network. According to the invention, the optimization information is defined in a centralized manner in the network management center and the nodes apply the results of this centralized optimization according to their own condition. The invention provides the advantage that the operation of individual nodes in setting up connections is very fast. Moreover, a fair distribution of network resources among users is achieved.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for routing in an ATMnetwork as defined in the preamble of claim 1 and to a system forrouting in an ATM network as defined in the preamble of claim 7.

BACKGROUND OF THE INVENTION

[0002] In prior art, several routing methods used in ATM networks(Asynchronous Transfer Mode, ATM) are known, such as the PNNI standard(Private Network-Node Interface, PNNI) by ATM Forum and the methodpresented in patent publication EP 0 814 583A2. Prior-art methods can bedivided into two groups. For example, the above-mentioned methodsrepresent shortest-path routing methods, which are derived from therouting methods used in data networks. Their aim is to define theshortest route between two nodes, i.e. e.g. the route with the smallestdelay. However, in ATM networks minimising the delay is not of suchessential importance as in traditional data networks because the ATMservice categories define the scope for the delay.

[0003] Another known group of routing methods are the methods based onLLR algorithms (Least Loaded Routing, LLR), which are used in thepresent-day telephone network. They involve the problem that a directconnection is assumed to exist between all nodes in the network.Moreover, they do not take into account the asymmetry which is typicalof ATM connections. In ATM connections, outgoing traffic is often only afraction of incoming traffic.

[0004] Both methods have the drawback that demanding and time-consumingoptimisation calculations have to be carried out in each node of thenetwork. Therefore, the nodes need a large processing capacity andcomplex software. In addition, complete information about the conditionof each link in the network has to be maintained in each node.Collecting this information and keeping it up to date requires a largevolume of signalling traffic, thus wasting network resources.

BRIEF DESCRIPTION OF THE INVENTION

[0005] The object of the present invention is to disclose a new type ofmethod and system to eliminate the drawbacks mentioned above.

[0006] A specific object of the present invention is to disclose arouting method and system in which optimal routes are determined in acentralised manner and the nodes apply the results of this centralisedoptimisation according to their own condition.

[0007] As for the features characteristic of the present invention,reference is made to the claims.

[0008] In the system of the invention for routing in an ATM networkcomprising a number of nodes connected to each other by links, a networkmanagement centre being connected to said ATM network, an ATM call isrouted from a node acting as originating point to a node acting asterminal point. The ATM call is e.g. a voice call or a connection fortransmitting data, video or equivalent. According to the invention,optimisation information is determined in a centralised manner e.g. inthe network management centre. Optimisation information refers tooptimal allocation among the routes available. This optimisationinformation is transferred to the nodes, which apply it in the routingin accordance with their own condition.

[0009] As compared with prior art, the present invention has theadvantage that individual nodes can function very fast in setting upconnections as they do not have to perform any complex optimisationcalculations and they do not have to collect and maintain any statusdata regarding all other links in the network. Moreover, as alldemanding functions are performed in a single centralised location,control is easier. Still, individual nodes work so independently thateven if all the means used for optimisation should fail, the networkwould still continue functioning.

[0010] A further advantage of centralised optimisation is that thesituation can be optimised with regard to the whole network by makinguse of an anticipated condition of the network as well. This makes itpossible to avoid situations where an individual node could block theentire network, as is fully possible in prior-art methods. In addition,in the method of the invention, a connection request is rejected if aglobal optimisation result so demands. This allows a fair distributionOf network resources between users. Moreover, the method of theinvention requires only small changes in existing nodes. in anembodiment of the invention, the traffic in the network is divided intocategories, the parameters for which are traffic matrix, symmetrymatrix, service quality and the return for each connection, a connectionbeing understood as an originating point-terminal point pair. Thetraffic matrix contains an estimate of the capacity required for theconnections, and this is defined by the operator on the basis ofexperience. The symmetry matrix defines the ratio of incoming data tooutgoing data. Optimisation aims at minimising the sum of rejectedcapacity for all traffic categories and all connections in eachcategory, weighted by the returns obtained from the connections.Rejected capacity refers to the difference between requested andallocated capacity. Moreover, the capacity of the links of the networkmust not be exceeded.

[0011] In an embodiment of the invention, the optimisation informationis so defined that the sum of rejected capacity for the connections ineach traffic category does not exceed a predetermined limit for thecategory.

[0012] In an embodiment of the invention, the optimisation informationis so defined that the rejected capacity for each connection does notexceed a predetermined limit.

[0013] In an embodiment of the invention, the nodes maintain statisticsabout the capacity required by the connection requests they receive.This statistical information is sent to the network management centre,and it is utilised in defining the optimisation information.

[0014] In the following, the invention will be described by the aid of afew examples of its embodiments with reference to the attached drawing,wherein

BRIEF DESCRIPTION OF THE DRAWING

[0015]FIG. 1 presents an embodiment of the system of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016] In FIG. 1, an embodiment of the system of the invention isillustrated. An ATM network 1 and a network management centre 2 areconnected together. The ATM network comprises a plurality of nodes 100,101, . . . , 10 n, which are connected to each other via links 110, 111,. . . , 11 n. When an ATM call is to be started e.g. from node 100 tonode 103, a procedure for determining an optimal route for the ATM callis activated. According to the invention, optimal routes are determinedin a centralised manner in the network management centre 2, and thenodes 100, 101, . . . , 10 n apply the results of this optimisation inaccordance with their own condition. In addition, the nodes maintainstatistics about the numbers of connection requests they receive, whichare then transferred to the network management centre. This statisticalinformation is utilised in the following optimisation calculations.

[0017] The optimisation aims at determining an optimal allocation ofcapacity among the routes available. The operator has the requiredinformation regarding network topology and the capacity of each link inthe network. Moreover, traffic service categories K, the parameters ofwhich are traffic matrix T, symmetry matrix S, service quality Q and thereturn R obtained from each connection, i.e. each origin-terminal pair,as well as the routes available for each service category have beendefined. The optimisation can be expressed in a mathematical form e.g.as presented below. In solving the problem, it is possible to utilisee.g. a Simplex algorithm known in itself. The capacity required by theconnection requests received by each node can be used to update anestimate of the traffic matrix.$\min {\sum\limits_{c}{\sum\limits_{\forall{({s,d})}}{\left( r_{s\quad d} \right)^{c}\left( {1 + s_{s\quad d}} \right)b_{s\quad d}\quad {so}\quad {that}}}}$$\quad {\begin{matrix}{{{\sum\limits_{k}\left( p_{s\quad d}^{k} \right)^{c}} = {\left( t_{s\quad d} \right)^{c} - \left( b_{s\quad d} \right)^{c}}}\quad} & {\quad {{\forall\left( {s,d} \right)},{\forall c}}} \\{{\sum\limits_{{({s,d})},k,c}{\left( \left( a_{s\quad d}^{k} \right)^{i\quad j} \right)^{c}{\left( p_{s\quad d}^{k} \right)\quad}^{c}}} \leq c^{\quad {i\quad j}}} & {\quad {\forall{\left( {i,j} \right) \in \quad A}}} \\{\quad {{\sum\limits_{({s,d})}\left( b_{s\quad d} \right)^{c}} \leq {F{\sum\limits_{({s,d})}\left( t_{s\quad d} \right)}}}} & {\quad {\forall\quad c}} \\{\left( b_{s\quad d} \right)^{c} \leq {f_{s\quad d}\left( t_{s\quad d} \right)}^{c}} & {{\forall\left( {s,d} \right)},{\forall c}}\end{matrix},}$

[0018] where

[0019] Parameters:

[0020] N number of links

[0021] A number of links

[0022] T^(c)={(t_(sd))^(c)} traffic matrix for category c

[0023] S^(c)={(s_(sd))^(c)} symmetry matrix for category c

[0024] (r_(sd))^(c) return from connection s-d in category c

[0025] f_(sd) equity limit, i.e. upper limit for rejected load ofindividual connections

[0026] F equity limit for category, i.e. upper limit for rejected loadin each category

[0027] ((a^(k) _(sd))^(y))^(c) link-path case parameter:$\left( \left( {a\quad}_{s\quad d}^{k} \right)^{i\quad j} \right)^{c} = \left\{ \begin{matrix}{1,{{if}\quad {path}\quad k\quad {for}\quad {connection}\quad s\text{-}d\quad {in}\quad {category}}} \\{c\quad {uses}\quad {link}\quad \left( {i,j} \right)} \\{S_{s\quad d},{{if}\quad {path}\quad k\quad {for}\quad {connection}\quad s\text{-}d\quad {in}\quad {category}}} \\{c\quad {uses}\quad {link}\quad \left( {j,i} \right)} \\{0,{otherwise}}\end{matrix} \right.$

[0028] Variables:

[0029] (p^(k) _(sd))^(c) capacity allocated forward rate connection s-don path k in category c in forward direction

[0030] (b_(sd))^(c) rejected load for connection s-d in category c

[0031] In other words, the aim is to minimise the sum of rejectedcapacity in each traffic category and for all connections in eachcategory, weighted by the returns obtained from the connections. Afurther aim is to ensure that the sum of rejected capacity for theconnections in each traffic category will not exceed a limit specifiedfor the category, and that the rejected capacity for each connectionwill not exceed a predetermined limit. Furthermore, the capacity of thelinks in the network must not be exceeded.

[0032] The optimisation result is transferred to the nodes, which applyit in routing according to their own condition. Routing is effected e.g.according to the following algorithm.

[0033] Step 0: Reset status variables r₁ expressing the used-upproportion of the capacity for optimal route no. i to zero.

[0034] Step 1: In the case of an incoming ATM call, go on to step 2; atthe end of an existing ATM call, go to step 4.

[0035] Step 2: Route the incoming ATM call via the path for which p₁−r₁is maximised, where p₁ is the capacity allocated for path i duringoptimisation.

[0036] Step 3: If the ATM call is accepted, then add the capacityallocated for it to r₁ and go on to Step 1. Otherwise repeat Step 1 tofind the next path. If all paths for an optimal solution have beentried, then block the incoming ATM call.

[0037] Step 4: Subtract the capacity allocated for the terminating callfrom r₁ and go on to Step 1.

[0038] Thus, a connection request is rejected if the global optimisationresult requires rejection. This allows a fair distribution of networkresources among the users.

[0039] The invention is not restricted to the examples of itsembodiments described above, but many variations are possible within thescope of the inventive idea defined by the claims. For instance, theoptimisation can be implemented using a non-linear target function.

1. Method for routing in an ATM network (1) comprising a plurality ofnodes (100, 101, 102, . . . , 10 n) connected to each other via links(110, 111, 112, . . . , 11 n), a network management centre (2) beingconnected to said ATM network (1), in which method an ATM call is routedfrom an originating node to a terminal node, characterised in thatoptimisation information is defined in a centralised manner; theoptimisation information is transferred to the nodes (100, 101, 102, . .. , 10 n); and the ATM call is routed in the originating node using theoptimisation information and local status information.
 2. Method asdefined in claim 1, characterised in that the optimisation informationis so defined as to minimise the sum of rejected capacity for trafficcategories and for the connections in each category, said sum beingweighted by the returns obtained from the connections.
 3. Method asdefined in claim 1 or 2, characterised in that the optimisationinformation is so defined that the sum of rejected capacity for theconnections in each traffic category does not exceed a predeterminedlimit for the category concerned.
 4. Method as defined in any one of thepreceding claims 1-3, characterised in that the optimisation informationis so defined that the sum of rejected capacity for each connection doesnot exceed a predetermined limit.
 5. Method as defined in any one of thepreceding claims 1-4, characterised in that the optimisation informationis defined using the capacity required by the connection requestsreceived by the nodes.
 6. Method as defined in any one of the precedingclaims 1-5, characterised in that the optimisation information isdefined in the network management centre (2).
 7. System for routing inan ATM network (1) comprising a plurality of nodes (100, 101, 102, . . ., 10 n) connected to each other via links (110, 111, 112, . . . , 11 n),a network management centre (2) being connected to said ATM network (1),in which system an ATM call is routed from an originating node to aterminal node, characterised in that the system comprises optimisationmeans (21) for centralised definition of optimisation information; thesystem comprises means (21) for transferring the optimisationinformation to the nodes (100, 101, 102, . . . , 10 n); and the systemcomprises means (100, 101, 102, . . . , 10 n) for routing the ATM callin the originating node using the optimisation information and localstatus information.
 8. System as defined in claim 7, characterised inthat the system comprises means (21) for defining the optimisationinformation so as to minimise the sum of rejected capacity for trafficcategories and connections in each category, said sum being weighted bythe returns obtained from the connections.
 9. System as defined in claim7 or 8, characterised in that the system comprises means (21) fordefining the optimisation information so that the sum of rejectedcapacity for the connections in each traffic category does not exceed apredetermined limit for the category concerned.
 10. System as defined inany one of the preceding claims 7-9, characterised in that the systemcomprises means (21) for defining the optimisation information so thatthe sum of rejected capacity for each connection does not exceed apredetermined limit.
 11. System as defined in any one of the precedingclaims 7-10, characterised in that the system comprises means (21) forutilising the capacity required by the connection requests received bythe nodes (100, 101, 102, . . . , 10 n) in defining the optimisationinformation.
 12. System as defined in any one of the preceding claims7-11, characterised in that optimising means (21) are disposed inconjunction with the network management centre (2).